From time to time the need arises for a welding wire or continuous arc electrode that is usable to weld alloys having rather specific characteristics. The situation is exemplified by a need that existed in relation to catalytic converters for automotive use and other high temperature anti-pollution devices. Specifically, proposals have been made to reduce the volume of air pollutants from automotive engines by catalytic converters that process the engine exhaust stream. One of the difficulties encountered in the course of developing a commercially practical catalytic converter relates to the highly-corrosive nature of the exhaust stream. A solution to that problem involves the use of corrosive-resistant, though relatively inexpensive stainless steel alloys, notably Type 409M stainless steel.
Although Type 409M stainless steel is very resistant to corrosion, and relatively inexpensive, it also is substantially nonductile. Consequently, the use of the material in fabricated structures has previously been quite limited and efforts to draw welding wire for the material presents considerable problems. Specifically, forming welding wire from such alloys directly is not feasible because the material is not sufficiently ductile to be drawn. That is, a billet of 409M stainless steel would require formation into a wire for effective use in arc welding processes. The problems attendant forming a billet of such alloy into a usable wire are strongly compelling against pursuing such a process.
The difficulty of forming welding wires, as from billets of 409M stainless, suggested the possibility of fabricating wire electrodes. Accordingly, wires were fabricated to contain components of an alloy as would be expected to form a satisfactory weld. However, repeated tests with such wires have been unsatisfactory. Substantial efforts to maintain the weld of sufficient strength, and outside the gamma loop (region of hardening), generally have been successful only with wires of relatively very high cost.
In general, the present invention is directed to an economical wire and process for effectively welding 409M stainless steel, which wire is in the form of a fabricated electrode, e.g. metallic strip formed into a sheath so as to enclose other desirable components for the composite wire. A characteristic of the fabricated wire of the present invention is that it forms a weld deposit that falls outside the gamma loop while containing a practical quantity of carbon for strength. The wire is attained, recognizing the economic significance of using relatively low (under 14% or 15% by weight) quantities of chrome. In the combination of components as defined and considered below, the need was discovered for an unconventionally very-large quantity of titanium to produce an electrode that may be effectively employed in gas-shielded arc welding.